IPA: /ˌɪrɪˈpleɪsəblɪ/
KK: /ɪrɪˈpleɪsəblɪ/
In a way that cannot be replaced or substituted; uniquely or singularly.
Her contributions to the project were irreplaceably valuable.
Irreplaceably → It is formed from "ir-" (meaning not) and "replace" (from Latin "replacere", meaning to place again) and "-ably" (meaning in a manner that can be). The word "irreplaceably" means in a manner that cannot be replaced or substituted.
Think of 'not' ('ir-') being able to 'place again' ('replace') — that's why irreplaceably means something that cannot be substituted.